Resistor unit



Jan. 3,1939. D. F. HAsTiNGs RES I STOR UNI T Filed Sept. 22, 1937Patented Jan. 3, 1939 PATENT OFFICE RESISTOR UNIT Donald F. Hastings,Fairlawn, N. J., assigner to Hardwick, Hindle, Inc., Newark, N. J.

Appuoation soptomberea 1937, soriolv No. 165,104

7 Claims.

readily understood by reference to the annexeddrawing, wherein:

Figure 1 is a plan viewof the completely assembled resistance unit, theouter covering over the resistance winding being omitted at the endsWhere the Winding is connected tothe terminals.

Figure 2 is an enlarged, longitudinal, sectional view through the leftend of the device shown in Figure 1.

Figure 3 is a view on the line 3 3 of Figure 2.

Figure 4 is a plan view of the filler strip used in mounting the contactferrule onto the resistance unit.

In the various views, wherein like numbers refer to corresponding parts,I is a core, preferably hollow to provide ventilation. The core is madeof high-heat-resisting and insulating material, preferably of ceramicnature, on which is located a Winding 2 of any satisfactory resistancewire. After the winding 2 is puton, it is preferably covered with avitreous enamel coating 3. On each end of the core I is mounted a bandferrule 4 which is preferably made of a non-corrosive material,-such asMone] metal, which has a low temperature coefficient of expansion.

In forming the ferrule or cup 4, the edge or rim 5 is preferably turnedover, as shown in Figure 2, to provide a smooth annular shoulder whichacts as a guide and stop for assisting in locating the unit on itsspring member mounting. The opposite end of the ferrule 4 has a ange 6of a width sufhcient to overlap the end of the core to mechanicallyprotect the core and at the same time x the location of the ferrule onthe core. In order to hold the ferrule 4 on .the end of the core I, ametallic filler strip 1, shown in detail in Figure 4, is used. The strip1 is provided with a plurality of spaced ribs or bosses 8 which areformed outwardly from the body of the strip 1, as more particularlyshown in Figure 2. The strip or shim 1 is preferably' made of relativelysoft metal having a high-temperature o9- eilicient of expansion, such ascopper. The shim or filler strip is preferably provided with a pluralityof wire-wrapping cleats 9, the function of which will be presentlydescribed.

The thickness of the strip 1 and the height of 5 o the bosses or ribs 8are made compatible with the internal diameter of the ferrule 4 and theoutside diameter of the end of the core I, but I have found, inpractice, that by using the copper strip having a thickness of .008" to.010", and bosses 10 or ribs having a total depth of approximately.020", that when the ferrule 4 is forced into place over the end of thecore I, as shown vin Figure 2, it being understood that the strip 1 isfolded up circularly and placed within the fer- .15 rule 4 before thesame is forced over the end of the core I, this type of filler strip orshim com-- pensates for normal variations in the outside diameter of thecore I and inside diameter ofthe remue 4, it boing understood that theforruie 4 2 is made to have an internal diameter compatible with thesize of the core I to be used, the idea being to secure a tight fitbetween the ferrule and the end of the core I, through the medium of afiller strip as heretofore described. 25

After the ferrule 4 and its associated filler strip have been assembledto the core I, one end of the 'vinding 2 is wrapped around a cleat 9,preferabiy in a diagonal or crosswise manner, after which the Wire isbrazed or soldered with hard 30 solder to the cleat 9 which, as shown inFigures 1 and 2, projects a short distance beyond the rim 5 of theferrule. It sometimes occurs that the resistance 2 is required to bevery accurate and even an additional inch or half-inch of wind- 35 ingis objectionable. Therefore, to better meet this condition, a pluralityof cleats 9 are provided on the strip 1 so that the resistance wire maybe terminated at any one of these cleats, it being understood that Iprefer to put the wind- 40 ing 2 onto the core I after the ferrules 4have been mounted in position.

I have found that by constructing the ferrule 4 and shim 1 of thematerials and mounting them in the manner heretofore described, pro- 45vides such a -satisfactory union that after the vitreous enamel 3 isapplied to the winding 2, the high temperature required for firing orbaking this vitreous enamel covering, will not loosen the union. In theapplication of the outer covering, 50 this is preferably extended tocompletely cover the cleats 9 and the connection of the winding thereto,as well as to seal the joint around the rim 5, somewhat as indicated atI0 in Figure 2. While I have specied an outer covering of vitre- 55 ousenamel, for certain purposes some other type of covering, such ascementor insulating varnish, may be used.

In the past it has been the practice to connect the end of theresistance winding to a stranded copper Wire which is also Wrappedaround the core, and then connect this copper Wire to a clip on theferrules which are held to the core by cementing or by a through bolt;but by my method of construction and assembly as described herein, Ihave greatly simplified and improved the general arrangement of theresistance unit.

What I claim is:

1. A resistance unit including a core member of heat-resisting andinsulating material having a winding thereon but spaced from the ends ofthe core and covered with a coating of baked vitreous material, ametallic band ferrule located on each end of the core adjacent thetermination of the winding, and means for holding the ferrule in place,said means comprising a metallic ller strip coiled to the approximateinternal diameter of the ferrule and located therein, said filler striphaving a plurality of transverse ribs normally projecting from the planeof the strip so when the core ends are forced into the ferrules the ribsprovide suficient .gripping to hold the ferrules securely in place atall times, including that of baking thel covering, and means forelectrically connecting the ends of the Winding to the feriules beforethe said baked coating is applied.

2. A resistance unit as set forth in claim 1, further characterized inthat one edge of the filler strip is provided with at least onewire-Wrapping cleat which projects beyondl the inner end of the ferruleto receive one end of the Winding.

3. A resistance unit as set forth in claim 1, further characterized inthat the ferrule comprises a cup of non-corrosive metal having a lowtemperature coefficient of expansion, While the filler strip is ofrelatively soft metal having a high temperature coeiicient of expansion.

4. A resistance unit as set forth in claim 1, further characterized inthat the ferrule comprises a cup of drawn Monel metal having an end angeof a Width to overlap the core and a turned over.

rim, vvhile the ller strip is of copper having a plurality of projectingcleats for wrapping the end of the winding therearound.

5. A resistance unit including a tubular core of ceramic' materialhaving a Winding thereon but spaced from the ends of the core, ametallic band ferrule located on each end of the core adjacent an end ofthe winding, a metallic filler strip of good current-conducting materialhaving a plurality of normally transverse ribs, coiled Within theferrule, the ribs acting to take up Variations Within limits in theoutside diameter of the core ends and inside diameter of the ferrules,and to hold the ferrules securely and permanentlyz in place on the corewhen the core ends and ferrules are pressed into operative position,said ller strip having at least one Wire-attaching cleat projectingbeyond the inner end of its associated ferrule for attachment of an endof the winding thereto.

6. A resistance unit as defined in claim 5, further characterized inthat the band ferrules are made of metal having a low temperaturecoeicient of expansion, While the ller strips have a high temperaturecoeicient of expansion.

7. A resistance unit including a core member of heat-resisting andinsulating material having a winding thereon but spaced from the ends ofthe core, a metallic band ferrulc located on each end of the coreadjacent the termination of the Winding, and means for permanentlyholding the ferrule in place, said means comprising a metallic fillerstrip arcuately fitting within the ferrule, said strip carrying meansprojecting from the plane of the strip so when the core ends are forcedinto the ferrules said means carried on the strip provide sufficientgripping to hold the ferrules securely in place, and means forelectrically connecting the ends of the' Winding to the ferrules, so theresistance of the unit will be very accurate, said means comprising aplurality of arcuately arranged cleats integral with the strip andprojecting beyond the inner edge of its associated ferrule, whereby acleat may be selected for attachment on the end of the Winding whichwill give the desired resistance to the unit.

DONALD F. HASTINGS.

